Diagnosis System

DESCRIPTION
1. When troubleshooting OBD II vehicles, the only difference from the usual troubleshooting procedure is to connect an OBD II scan tool complying with SAE J1987 or a intelligent tester to the vehicle, and read off various data output from the vehicle's ECM.
2. OBD II regulations require that the vehicle's onboard computer illuminate the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in the computer itself or in the drive system components which affect the vehicle emissions. In addition to illuminating the MIL when a malfunction is detected, the applicable DTCs prescribed by SAE J2012 are recorded in the ECM memory (See DIAGNOSTIC TROUBLE CODE CHART ).
  If the malfunction does not occur in 3 consecutive trips, the MIL goes off but the DTCs remain in the ECM memory.
  
  Fig 1: Identifying MIL (Malfunction Indicator Lamp)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. To check the DTCs, connect the OBD II scan tool or intelligent tester to the DLC3 of the vehicle. The OBD II scan tool or intelligent tester also enables you to erase the DTCs and check freeze frame data and various forms of engine data (For operating instructions, see the instruction book).
4. The DTCs include SAE controlled codes and Manufacturer controlled codes. SAE controlled codes must be set as prescribed by the SAE, while Manufacturer controlled codes can be set freely by a manufacturer within the prescribed limits (See DIAGNOSTIC TROUBLE CODE CHART ).
5. The diagnosis system operates in "normal mode" during the normal vehicle use. In normal mode, "2- trip detection logic" is used to ensure accurate detection of malfunction. "Check mode" is also available to technicians as an option. In check mode, "1-trip detection logic" is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent malfunction.
6. *2 trip detection logic: When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). IF the ignition switch is turned off and then turned on (IG) again, and same malfunction is detected again, the MIL will illuminate.

INSPECT THE DLC3

The vehicle's ECM uses ISO 9141-2 for communication. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 9141-2 format.

Terminals of DLC 3

Fig 2: Identifying DLC3 Terminal Arrangement

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

SYMBOL AND TERMINAL NO. REFERENCE

Symbol	Terminal No.	Name	Reference Terminal	Result	Condition
SIL	7	Bus "+" line	5 - Signal ground	Pulse generation	During transmission
CG	4	Chassis ground	Body ground	Below 1	Always
SG	5	Signal ground	Body ground	Below 1	Always
BAT	16	Battery positive	Body ground	11 to 14 V	Always

HINT:

If your display shows UNABLE TO CONNECT TO VEHICLE when you have connected the cable of the OBD II scan tool or intelligent tester to the DLC3, turned the ignition switch to the ON position and operated the scan tool, there is a problem on the vehicle side or tool side.

If the communication is normal when the tool is connected to another vehicle, inspect the DLC3 on the original vehicle.
If the communication is still impossible when the tool is connected to another vehicle, the problem is probably in the tool itself, so consult the Service Department listed in the tool's instruction information.

CHECK BATTERY VOLTAGE
1. Measure the battery voltage.
  Battery voltage: 11 to 14 V
  
  If voltage is below 11 V, replace the battery before proceeding.
CHECK MIL
1. The MIL comes on when the ignition switch is turned to the on position and the engine is not running.
  HINT:
  
  If the MIL does not light up, troubleshoot the combination meter.
2. When the engine is started, the MIL should go off. If the lamp remains on, it means that the diagnosis system has detected a malfunction or abnormality in the system.